This invention pertains generally to radar signal processing techniques and in particular to a signal processing technique for reducing glint and cross-polarization errors associated with the radar returns from an extended target.
As is known, the angular location of an extended complex target measured by a radar is partially dependent upon the relative phases and amplitudes of the return signals from different points on such a target. Relative motion between the radar and such a target then causes a change in the aspect angle of the target, with the result that the relative phases and amplitudes of the return signals change in a random way to cause the measured angular location to move in an unpredictable fashion about the centroid of the illuminated area of an extended complex target. Such unpredictable movement of the measured angular location is commonly referred to as "glint," or "angle noise," and may be so large that the measured angular location of a target may even lie outside the extremities of the target.
A moment's thought will make it clear that the presence of glint makes it difficult to generate proper guidance signals for a guided missile, especially in the terminal phase of flight of such a missile toward an extended complex target. In such a situation, the occurrence of glint makes it appear that the target has performed a maneuver which it has not; in consequence, the flight path of the guided missile will be incorrectly adjusted to account for a nonexistent maneuver of the target. As a matter of fact, the guided missile may be called upon to perform such violent maneuvers that aerodynamic or tracking capabilities may be exceeded so that a successful intercept may not be carried out.
It is also known that the effect of the radome and antenna (used in all radar-guided missiles) on incident radio frequency energy may cause angle noise, or glint. For convenience, the phenomenon will be called "polarization modulation." That is to say, when return signals from an extended complex target pass through any known type of radome to an antenna, originally depolarized components of such signals may be transformed in an unpredictable manner to cross-polarized and co-polarized components. Again, the deleterious effect of any such unpredictable change must be reduced, if not eliminated, to achieve the desired degree of accuracy in guidance of a guided missile.